Jordan P. Bloom and Arminder S. Jassar
This chapter is a revision and update of that included in previous editions of the TSRA Review written by Joshua B. Goldberg (2nd edition) and Stephen H. McKellar (1st edition).
Background
Ascending aortic aneurysms are a result of a multitude of pathologic processes which cause dilation and wall thinning, putting patients at risk of catastrophic complications such as rupture or dissection. With fixed loading conditions, a larger aneurysm results in greater wall tension (Law of Laplace: tension = radius x pressure) thus carries a higher rupture risk. Other risk factors for aneurysm rupture include growth rate, smoking, hypertension, inflammation and possibly fluoroquinolone usage. This chapter will discuss the pathophysiology, clinical presentation, diagnosis, treatment and current guidelines for management of ascending aortic aneurysms.
Pathophysiology
The embryologic origin of the ascending aorta and arch is different from that of the rest of the thoracic aorta thus is subject to different pathologic processes that may lead to aneurysmal degeneration. The ascending aorta smooth muscle cells arise from neural crest cells while the descending aorta arises from paraxial mesoderm. These smooth muscle cells are responsible for secreting many of the proteolytic factors implicated in aneurysm formation. When compared to the rest of the aorta, the ascending aorta contains a preponderance of elastin. Disruption or degradation of the elastin is a primary cause of aneurysmal degeneration of the ascending aorta as opposed to atherosclerosis causing aneurysms of the descending thoracic and abdominal aorta. There are two main etiologies of ascending aortic aneurysms: connective tissue disorders and degenerative (also called sporadic or idiopathic). Other rarer causes of aneurysms are trauma and aortitis (infectious or inflammatory).
Connective tissue disorders
Patients with connective tissue disorders with ascending aortic aneurysms tend to present at a younger age, experience more rapid aortic growth, are more likely to present with aortic dissection and have more associated extra-aortic vascular pathology. It is recommended that patients with connective tissue disorders undergo more aggressive screening regimens and earlier prophylactic surgical intervention.
- Marfan syndrome. Marfan syndrome is caused by an autosomal dominant mutation of the fibrillin-1 (FBN1) gene which functions as a TGF-β receptor. Marfan aortas have abnormal collagen crosslinking and elastin fragmentation believed to be caused by increased TGF-β activity in the aortic wall. Histologic examination reveals cystic medial degeneration. Marfan’s patients tend to present with isolated root aneurysms.
- Loeys-Dietz syndrome. This syndrome is caused by mutations in the genes that encode TGF-β receptors 1 and 2 and are associated with a complex phenotype (hypertelorism, bifid uvula or cleft palate, and arterial tortuosity), which also includes early aneurysmal degeneration of the aorta.
- Ehlers-Danlos type IV. This disease is caused by a defect in procollagen III synthesis that results in remarkably thin and aneurysmal arteries that are prone to rupture. Classically affecting the carotids or mesenteric vessels, this process does also affect the aortic arch and the ascending aorta.
- Turner syndrome. This is a gonadal dysgenesis syndrome characterized by a 45X karyotype resulting in females with ovarian failure and characteristic features such as a webbed neck, short stature, and low-set ears. Ten to 25% of patients have bicuspid aortic valves, 8% will have coarctation, and approximately 33% will have aortic dilatation. Aneurysms associated with Turner’s are typically seen in the patients with bicuspid aortopathy.
Non-syndromic disorders
- Familial thoracic aortic aneurysm and dissection (TAAD). Familial TAAD patients do not meet strict inclusion criteria for the aforementioned CTDs yet have a family history of aneurysmal disease. These patients tend to present earlier in life when compared to degenerative patients and most commonly have ascending aortic aneurysms (80%).
- . Approximately 1-2% of the population has bicuspid aortic valves making it the most common congenital heart defect. While not always considered a classic connective tissue disorder, bicuspid aortic valves are familial and, histologically, are similar to other connective tissue disorders with elastin fragmentation and fibrillin deficiency. The reported prevalence of aortic dilation in patients with bicuspid aortic valves ranges from 20-84%. There are three distinct aortic phenotypes associated with bicuspid aortic valves. The most common (Type I) is ascending aortic dilation with mild to moderate root dilation and is associated with right-left fusion and aortic stenosis. Type II is isolated ascending dilation without root dilation and is associated with right-noncoronary cusp fusion. The rarest (Type III) is an isolated root aneurysm.
Sporadic or degenerative
Degenerative ascending aortic aneurysms are the result of atherosclerosis and hypertension and manifest as asymmetric aneurysmal degeneration of the aorta. These aneurysms tend to present in older patients and have a rate of enlargement of ~0.1 cm/year.
Traumatic aneurysm
Traumatic aneurysmal disease is rare and is typically the result of a missed aortic injury after a traumatic event. This is most commonly from a non-penetrating etiology however has also been described in penetrating trauma. In the modern era, with the use of CT imaging, most of these aortic injuries will present at the time of evaluation.
Aortitis (inflammatory/infectious)
Rarely an inflammatory condition can be the cause of aneurysmal degeneration of the aorta. Studies quote inflammatory changes found on pathologic analysis in around 3% of surgical
specimens. These can be further subdivided into infectious vs. noninfectious. Infectious causes include bacterial inoculation, bacteremia, septic embolism, or contiguous infection. Non-infectious aortitis may be related to Takayasu arteritis, giant cell arteritis, immunoglobulin G4-related disease-related aortitis, ankylosing spondylitis, relapsing polychondritis, or Cogan syndrome.
Clinical presentation
Ascending aortic aneurysms are generally incidentally discovered during imaging for other issues. Patients with symptomatic aneurysms can present with pain or sudden death caused by rupture, or symptoms caused by compression of adjacent structures such as voice changes (recurrent laryngeal nerve).
Diagnosis
The diagnosis of ascending aortic aneurysms is largely based on imaging. The most commonly used diagnostic modalities are echocardiography and CT. Echocardiography is limited by inter-observer variability and the inability to adequately image the distal ascending aorta and the aortic arch. CT angiography allows more precise measurements with less variability in technique, resulting in a more reliable comparison of aneurysm growth over time. Moreover, with the addition of ECG gating, data can be acquired only during a specified portion of the cardiac cycle, typically during diastole when the heart is not moving which can significantly enhance the diagnostic value of the study. It does, however, come at the expense of ionizing radiation and IV contrast loads. Societal guidelines recommend that measurements of aortic diameter should be taken at reproducible anatomic landmarks and perpendicular to the axis of blood flow (LOE C).
Treatment and Guidelines
Symptomatic ascending aortic aneurysms require emergent surgical replacement to prevent an aortic catastrophe. Indication for surgical replacement of asymptomatic ascending aortic aneurysms depends on the size and etiology of the aneurysm. Additionally, the ascending aortic aneurysm is often replaced during concomitant cardiac surgery such as aortic valve replacement, even though strict size thresholds may not be met. Commonly accepted criteria based on the US guidelines for surgical intervention of isolated ascending aortic aneurysms are shown in the table below.
| Aneurysm Etiology | Intervention Size Threshold (Class/LOE) |
| Any | Symptoms due to aneurysm Growth rate >0.5 cm/year (IIa/B) Concomitant cardiac surgery: 4.5 cm (IIa/C) |
| Sporadic/Degenerative | 5.5cm (I/B) |
| Bicuspid Aortopathy | No risk factors: 5.5 cm (I/B) With risk factors: 5 cm (IIa/B) Root phenotypeAortic RegurgitationUncontrolled HTNFamily h/o dissection or sudden deathGrowth >3 mm/year Low surgical risk with experienced team: 5 cm (IIb/C) |
| Marfan’s / other connective tissue diseases | 5 cm (IIa/B) Family history of dissection, or other high-risk features: 4.5 cm |
| Loeys-Dietz or TGFBR1/2 mutations | 4.2 cm (IIb/C) |
| Inflammatory | Same as Sporadic/Degenerative |
These recommendations for repair are based mostly on natural history studies of sporadic ascending aortic aneurysms in which the risk of rupture increased dramatically at 6 cm. However, it is important to note that adverse aortic events can occur at diameters less than 5.5 cm in both the syndromic and sporadic aneurysm populations. While the criteria represented above reflect the most recent guidelines, discussion continues regarding the size criteria for replacement.
Growth rate is another important consideration. In general, isolated degenerative ascending aortic aneurysms have an average expansion rate of 0.1 cm per year. Familial patients tend to grow faster with an average expansion rate of 0.2 cm per year. Marfan syndrome is associated with average expansion rates up to 0.3 cm per year. TAAs patients with Loeys-Dietz syndrome can expand very rapidly at up to 1.0 cm per year. Aortic replacement is considered when aorta grows >5 mm/year.
Other scenarios that may promote hemodynamic lability such as pregnancy should be considered when determining need for aortic replacement. Pregnant women with aortic aneurysms should be delivered where cardiothoracic surgery is available (Class I, LOE C). Fetal delivery via cesarean section is reasonable for patients with significant aortic enlargement, dissection, or severe aortic valve regurgitation (Class IIa, LOE C). If progressive aortic dilatation and/or advancing aortic valve regurgitation are documented, prophylactic surgery may be considered (Class IIb, LOE C).
Finally, there has been growing interest in the indexing of aortic size to body surface area (BSA). In patients with short stature an aortic diameter/BSA >2.75 cm/m2 may be an indication for repair.
Surgical technique
Surgical repair involves replacement of the aneurysmal portion of the aorta with artificial graft and can be performed using standard CPB if the distal extent of the ascending aortic aneurysm allows sufficient room for placement of an aortic cross-clamp. However, if the distal extent of the ascending aortic aneurysm does not allow an aortic cross-clamp, hypothermic circulatory arrest is necessary to allow adequate resection. If the aortic root is aneurysmal, then aortic root can be replaced concomitantly, either with or without aortic valve replacement. If the aortic valve is diseased, but aortic root is not aneurysmal, aortic valve replacement can be performed while leaving the root alone.
Surveillance
Patients with ascending aortic aneurysms should be followed closely by a multidisciplinary team. In general, patients with aneurysmal disease should undergo a short interval follow-up echo or CT scan within 6 months of initial diagnosis. Depending on the rate of growth the next imaging interval can be extended to yearly. Aortic imaging is recommended for first-degree relatives of patients with thoracic aortic aneurysm and/or dissection to identify those with asymptomatic disease.
Suggested Readings
- Hiratzka LF, Bakris GL, Beckman JA, et al. 2010 ACCF/AHA/AATS/ACR/ASA/SCA/SCAI/SIR/STS/SVM guidelines for the diagnosis and management of patients with Thoracic Aortic Disease: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines, American Association for Thoracic Surgery, American College of Radiology, American Stroke Association, Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Society of Thoracic Surgeons, and Society for Vascular Medicine. Circulation. 2010;121(13):e266-369.
- Erbel R, Aboyans V, Boileau C, et al. 2014 ESC Guidelines on the diagnosis and treatment of aortic diseases: Document covering acute and chronic aortic diseases of the thoracic and abdominal aorta of the adult. The Task Force for the Diagnosis and Treatment of Aortic Diseases of the European Society of Cardiology (ESC). Eur Heart J. 2014;35(41):2873-926.
- Saliba E and Sia Y. The ascending aortic aneurysm: When to intervene? IJC Heart & Vasculature. 2015;6:91-100.
